Inkjet printing on glass or ceramic substrates has been known for some time. The printing process includes the distribution of ink containing inorganic pigment particles, solvents, sub-micron glass frit particles, and some other ink ingredients across a surface of a substrate. The sub-micron glass particles and inorganic pigments are later fused or fired into the substrate during the tempering or annealing process. The fusing of ink into the substrate supports the creation of vivid, durable designs that can last as long as the substrate itself.
The inks used for ceramic tile decoration have to satisfy several criteria. First, they must have the correct rheological and other properties such that they can be easy ejected from the nozzles of the inkjet printhead. The inks printed on a glass or ceramic substrate have to produce the desired final gloss, color and stability after application to the substrate and its further thermal processing and in particular firing.
Most of the currently used inks contain finely ground refractory inorganic pigments, synthetic nanoparticles, or soluble metal compounds. The formulation of inks for inkjet printing is challenging because not only must the ink maintain the desired final appearance, but it also has to maintain the physical properties that have been specially optimized for ink-jet printing. For example, the inks for printing on glass or ceramic surface have to utilize inorganic pigments, be sufficiently opaque, and may contain their own binder in the form of a glass frit. Because of these considerations they usually have a higher solids load then for example, ink for printing on paper. In order to avoid nozzle clogging, the pigment and glass frit particles are usually of sub-micron size. In the long term, such particle dispersions become not stable and tend to form sediments changing the density or the printed image and to some extent its color. Therefore, printers are required to include expensive and complex systems for constantly agitating and circulating the ink to prevent its separation.
Inkjet printing on glass or ceramic surfaces is an industrial glass and ceramics decoration process and maintenance of a stable ink and proper operating printer are paramount for successful penetration of the technology into the mainstream glass and ceramics industrial printing processes. In order to achieve optimal results the inkjet ink formulations have also to be matched to existing inkjet printheads. The industry would welcome improvements of the existing ink formulations as well as development of new inkjet ink formulations.